Our invention pertains to the field of lenses for use in optical and/or photonic apparatus. More particularly, it deals with novel reflective and catadioptric reflaxicon designs of our creation and their implementation in forms useful in such apparatus.
The term axicon generally refers to a specialized refractive lens type having a rotationally symmetric truly conical surface. Refractive axicons have been used in many optical applications and are relatively straightforward to fabricate. They have been used to image a point source as a line along the optical axis, or to transform a collimated laser beam into a ring. They have also been used to transform a Gaussian beam into an approximation of a Bessel beam.
A reflective axicon, termed “reflaxicon” was first proposed by Edmonds in 1973, who lightly explored it from a theoretical basis. (“The Reflaxicon, a New Reflective Optical Element, and Some Applications;” APPLIED OPTICS; Vol. 12, No. 8; August 1973). However, since then reflaxicons have found only limited tangible application in the optical arts.
From a theoretical standpoint, a reflaxicon is generally said to comprise a primary conical mirror 1 and a larger secondary conical mirror 2 located coaxially with respect to the primary mirror 1, as illustrated in FIG. 1A. The secondary mirror 2 is truncated so as to create an axial or central opening 2A with an inner diameter equal to or exceeding the base diameter 1A of the primary mirror 1. One of the usual functions of this combination, as illustrated in FIG. 1A, is to convert a solid light beam (such as a Gaussian intensity distribution laser beam) into a hollow beam in an essentially lossless manner. By converting a solid light beam into a ring, the reflaxicon accomplishes reflectively what an axicon accomplishes refractively. In addition, the half-angle theta 2 of the secondary cone 2 and the half-angle theta 1 of the primary cone 1, can be chosen so as to produce a converging, parallel, or diverging beam. Further, by pairing reflaxicons, a variety of other effects become theoretically possible, such as—for example—curving the initial secondary mirror 2 of a reflaxicon pair to compensate for non-diffraction limited beam divergence of incident light as illustrated in FIG. 1B. However, while the theoretical possibilities of reflaxicons have received some limited exploration, their practical application has been limited. Consequently, our designs represent a radical expansion in terms of the practical implementation and use of reflaxicons in optical systems as well as in their incorporation into optical and photonic apparatus.
To begin with, we have developed reflaxicons for practical use and implementation as both tightly or loosely toleranced optics for either imaging or non-imaging applications. Examples of applications for tightly toleranced optics for imaging include: diffraction limited relay objectives (finite conjugate imaging), diffraction limited microscope objectives (both finite and infinite conjugate imaging), diffraction limited high power laser focussing objectives, and laser beam delivery systems (afocal designs for beam expanders, pupil relays, and beam shaping systems). Examples of applications for loosely toleranced optics for imaging include: non-diffraction limited relay objectives (finite conjugate imaging), non-diffraction limited microscope objectives (both finite and infinite conjugate imaging), laser focussing objectives, and laser beam delivery systems. Examples of applications for loosely toleranced optics for non-imaging include: illumination and light concentration optics such as LED collection collimators, solar concentrators, and arrays of such elements. None of these applications for reflaxicons have received tangible development within the optical arts. In this context we have developed and invented structures based both on solid reflaxicons produced from optical glass (divided into either only purely reflective designs, or catadioptric designs operating on both refractive and reflective principles) and hollow reflaxicons (operating purely reflective), and various combinations of the foregoing.
The use of reflaxicons alone is an inherently beneficial development, as pure reflective optical systems are inherently free of chromatic aberrations. Moreover, our designs can, at their limits, be free of obscuration (a common problem in purely reflective systems). Alternatively, the amount of obscuration can be chosen to fit the application. In addition, our designs do not require beam splitters, tilted or decentered components, and are preferably axially symmetric, making them far simpler and easier to implement than typical all-reflective systems. Further details on the foregoing will be made plain in the drawing figures and detailed description that follow.